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.\" ========================================================================
.\"
.IX Title "DSA_generate_parameters 3"
.TH DSA_generate_parameters 3 "2014-07-11" "LibreSSL" "LibreSSL"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
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.nh
.SH "NAME"
DSA_generate_parameters_ex, DSA_generate_parameters \- generate DSA parameters
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 1
\& #include <openssl/dsa.h>
\&
\& int DSA_generate_parameters_ex(DSA *dsa, int bits,
\&                const unsigned char *seed,int seed_len,
\&                int *counter_ret, unsigned long *h_ret, BN_GENCB *cb);
.Ve
.PP
Deprecated:
.PP
.Vb 3
\& DSA *DSA_generate_parameters(int bits, unsigned char *seed,
\&                int seed_len, int *counter_ret, unsigned long *h_ret,
\&                void (*callback)(int, int, void *), void *cb_arg);
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
\&\fIDSA_generate_parameters_ex()\fR generates primes p and q and a generator g
for use in the \s-1DSA\s0 and stores the result in \fBdsa\fR.
.PP
\&\fBbits\fR is the length of the prime to be generated; the \s-1DSS\s0 allows a
maximum of 1024 bits.
.PP
If \fBseed\fR is \fB\s-1NULL\s0\fR or \fBseed_len\fR < 20, the primes will be
generated at random. Otherwise, the seed is used to generate
them. If the given seed does not yield a prime q, a new random
seed is chosen and placed at \fBseed\fR.
.PP
\&\fIDSA_generate_parameters_ex()\fR places the iteration count in
*\fBcounter_ret\fR and a counter used for finding a generator in
*\fBh_ret\fR, unless these are \fB\s-1NULL\s0\fR.
.PP
A callback function may be used to provide feedback about the progress
of the key generation. If \fBcb\fR is not \fB\s-1NULL\s0\fR, it will be
called as shown below. For information on the \s-1BN_GENCB\s0 structure and the
BN_GENCB_call function discussed below, refer to
\&\fIBN_generate_prime\fR\|(3).
.IP "\(bu" 4
When a candidate for q is generated, \fBBN_GENCB_call(cb, 0, m++)\fR is called
(m is 0 for the first candidate).
.IP "\(bu" 4
When a candidate for q has passed a test by trial division,
\&\fBBN_GENCB_call(cb, 1, \-1)\fR is called.
While a candidate for q is tested by Miller-Rabin primality tests,
\&\fBBN_GENCB_call(cb, 1, i)\fR is called in the outer loop
(once for each witness that confirms that the candidate may be prime);
i is the loop counter (starting at 0).
.IP "\(bu" 4
When a prime q has been found, \fBBN_GENCB_call(cb, 2, 0)\fR and
\&\fBBN_GENCB_call(cb, 3, 0)\fR are called.
.IP "\(bu" 4
Before a candidate for p (other than the first) is generated and tested,
\&\fBBN_GENCB_call(cb, 0, counter)\fR is called.
.IP "\(bu" 4
When a candidate for p has passed the test by trial division,
\&\fBBN_GENCB_call(cb, 1, \-1)\fR is called.
While it is tested by the Miller-Rabin primality test,
\&\fBBN_GENCB_call(cb, 1, i)\fR is called in the outer loop
(once for each witness that confirms that the candidate may be prime).
i is the loop counter (starting at 0).
.IP "\(bu" 4
When p has been found, \fBBN_GENCB_call(cb, 2, 1)\fR is called.
.IP "\(bu" 4
When the generator has been found, \fBBN_GENCB_call(cb, 3, 1)\fR is called.
.PP
\&\fIDSA_generate_parameters()\fR (deprecated) works in much the same way as for DSA_generate_parameters_ex, except that no \fBdsa\fR parameter is passed and
instead a newly allocated \fB\s-1DSA\s0\fR structure is returned. Additionally \*(L"old
style\*(R" callbacks are used instead of the newer \s-1BN_GENCB\s0 based approach.
Refer to \fIBN_generate_prime\fR\|(3) for further information.
.SH "RETURN VALUE"
.IX Header "RETURN VALUE"
\&\fIDSA_generate_parameters_ex()\fR returns a 1 on success, or 0 otherwise.
.PP
\&\fIDSA_generate_parameters()\fR returns a pointer to the \s-1DSA\s0 structure, or
\&\fB\s-1NULL\s0\fR if the parameter generation fails.
.PP
The error codes can be obtained by \fIERR_get_error\fR\|(3).
.SH "BUGS"
.IX Header "BUGS"
Seed lengths > 20 are not supported.
.SH "SEE ALSO"
.IX Header "SEE ALSO"
\&\fIdsa\fR\|(3), \fIERR_get_error\fR\|(3), \fIrand\fR\|(3),
\&\fIDSA_free\fR\|(3), \fIBN_generate_prime\fR\|(3)
.SH "HISTORY"
.IX Header "HISTORY"
\&\fIDSA_generate_parameters()\fR appeared in SSLeay 0.8. The \fBcb_arg\fR
argument was added in SSLeay 0.9.0.
In versions up to OpenSSL 0.9.4, \fBcallback(1, ...)\fR was called
in the inner loop of the Miller-Rabin test whenever it reached the
squaring step (the parameters to \fBcallback\fR did not reveal how many
witnesses had been tested); since OpenSSL 0.9.5, \fBcallback(1, ...)\fR
is called as in \fIBN_is_prime\fR\|(3), i.e. once for each witness.